The invention relates to a passenger-protection apparatus in the steering wheel of a motor vehicle.
Passenger-protection devices having a plurality of stages that can be deployed independently of one another, some having multi-chamber gas bags, are known from, for example, DE 195 41 924 A1, DE 196 11 718 A1 or DE 198 16 989 A1. In these instances, the level of the protective effect, particularly the inflation volume, is tailored to the severity of the accident.
A further type of passenger-protection apparatus having the function of protecting the passenger temporarily after the actual airbag deflates is known from, for example, DE 38 29 368 A1, DE 38 33 888 A1 or 92 11 421 U1. Gas-bag restraint systems of this nature have a gas bag with two chambers, with the first, larger chamber surrounding the second chamber, as shown in FIG. 5 of the present application. The first and second chambers must therefore be deployed simultaneously. The first chamber is limited by a wall made of a material having a greater gas permeability than the material limiting the second chamber. After the inflation, the inside, second chamber remains tautly filled longer, and, at least to some extent, protects the driver in the event of a second collision, particularly against the gas generator, which would otherwise be exposed once the first airbag has already deflated. The overlapping of the first and second chambers is disadvantageous from a manufacturing standpoint, and only permits the common deployment of the two airbags.
DE 41 29 314 A1 describes an airbag safety system in which, in addition to a first airbag for the driver, which has a first deployment device, a second airbag is provided for the passenger, which has a second deployment device; a third deployment device, which is delay-activated after the second deployment device, is also provided for the second airbag.
Passenger-protection apparatuses having an asymmetrical shape for providing the passenger with the greatest possible protection are known from DE 197 03 945 A1, JP 03-32956 and DE 297 00 804 U1.
In DE 197 03 945 A1, a plurality of superposed airbags is deployed simultaneously and filled with propellant in stages, as a function of their unimpeded expansion in the passenger space. The inflation process is supposed to be controlled as a function of the position and movement of the passenger, and the passenger""s head is also protected laterally. Controlling the filling procedure as a function of the unimpeded expansion is highly complicated, and does not appear feasible due to the extremely short filling time of a few milliseconds.
JP 03-32956 A1 describes a passenger-protection apparatus having a central, small gas bag with a conventional expansion length, and two external gas bags having a larger expansion length that offers lateral protection for the passenger""s head; the gas bags are filled simultaneously and from the same gas source. The gas bags are also connected among themselves by restraining straps, so a separate deployment is technically impossible.
In contrast, DE 297 00 804 U1 describes a wedge shape of the passenger-protection apparatus that becomes larger from the torso region to the head region.
A further problem in the activation of passenger-protection systems, which is known, for example, from DE 43 20 147 A1, is that the airbags are oriented with respect to a passenger who is assuming a predetermined restrained position, but at the moment of the accident, and the activation of the airbag, the passenger may be in a different position. If this airbag is immediately and fully activated during a crash, the very small initial distance between the airbag and the vehicle passenger may result in undesirable stress on the passenger. DE 43 20 147 A1 is intended to orient the passenger to the desired position by means of a first airbag stage, which means, however, that the passenger is also subjected to not entirely non-critical stress; furthermore, this orientation is hardly possible within the short time until the passenger impacts the front region, such as the steering wheel.
The xe2x80x9cout-of-positionxe2x80x9d passenger problem has also given rise to passenger-protection apparatuses that are described in, for example, DE 38 09 074 C2, DE 40 19 677 A1 or DE 40 23 109 A1, in which the sitting position of the relevant passenger in relation to the associated passenger-protection apparatuses is measured continuously. The times and/or the scope of the protective measures to be implemented are derived from these measurements.
If, however, the sitting position of the passenger must first be determined at the moment of the collision before an airbag can be deployed, a portion of the delay path remains unutilized.
In an analogous situation, DE 297 07 162 U1 describes a gas bag having at least one restraining strap with a tear-away seam; in an xe2x80x9cout-of-positionxe2x80x9d scenario, the gas bag is deployed as a function of the supplied gas pressure or gas quantity and reaches a first size, with the tear-away seams still being connected to the restraining straps, but then tearing due to a higher gas pressure or a larger gas quantity; the restraining straps keep the gas bag at a second size.
DE 196 28 837 A1 discloses an airbag in which the expansion length of a plurality of chambers increases in the direction of the passenger, that is, further gas bags are filled by means of laterally-extending supply hoses in the direction of the passenger in front of the first gas bag. The technical outlay for this feature is considerable, and positioning the additional gas bags is problematic.
DE 40 11 492 A1 also presents a passenger-protection apparatus in the steering wheel of a motor vehicle; in this case, at least one of the gas sources is disposed outside of the steering wheel, and the gas is supplied to the airbag disposed in the steering wheel by way of a pressure line. Gas sources considered for this apparatus are pyrotechnically-activated gas generators and compressed-gas cartridges, particularly those whose available gas quantities are metered by way of valves and distributors, and can be conducted into different airbags.
DE-OS 2 103 194 proposes providing a safety apparatus with an individual airbag that can be filled with compressed air from a compressed-air generator or container; when an impending collision is detected by so-called pre-crash sensors, the airbag is only partially filled, then completely filled upon impact. Otherwise, the partly-filled airbag must be emptied after a predetermined time.
A drawback of known passenger-protection apparatuses that employ airbags is that, without exception, the bags must possess a very large volume to offer the highest level of protection for the passenger, and thereby block the driver""s view of the traffic situation and prevent further steering actions. Airbags typically have a larger diameter than the actual steering wheel to be covered, as well as a relatively large expansion length in the direction of the driver. The driver can no longer see, and can no longer manipulate the steering wheel.
For this reason, in large-volume airbags, the deflation process must also be effected very rapidly by means of large discharge openings. This, again, stipulates a precise temporal determination of the deployment time, because if the airbag is deployed too early, the passenger is no longer adequately protected, whereas if the airbag is deployed too late, the passenger may be additionally injured.
It is the object of the invention to provide a technically simpler passenger-protection apparatus that permits an early, rapid protection of the passenger without severely impeding the driver""s reaction capabilities.
The above object generally is accomplished by the invention wherein a first stage of the deployment, a first airbag is provided, which has a specified shape and is supplied with a specified quantity of gas from a gas source such that, in the state in which the bag is filled with the quantity of gas, it has a collision zone that corresponds to the diameter of the steering wheel, and a short expansion length in the direction of the passenger relative to the distance between the collision zone and the passenger. The first, small airbag thus constitutes only a flat cushion that covers the steering wheel in the direction of the driver, and only insignificantly limits the driver""s visibility in a predetermined viewing region, and allows the driver to continue steering the vehicle.
According to the invention a second airbag likewise is provided for an independent second staghe of deployment that follows the first. This airbag enlarges the collision zone, and is therefore only deployed in the event of a particularly severe accident. The first and second airbags are deployed independently of one another, preferably with a time offset or, if the acceleration thresholds are exceeded one immediately after the other, as closely together as possible. Advantagous modifications of the basic invention are disclosed.
In the filled state, the second airbag laterally adjoins the first airbag in the manner of a hose, surrounding it annularly, at least partially but preferably completely. Together, the two airbags form a second, larger collision zone. The second airbag is preferably filled with a higher gas pressure, which compresses the first airbag such that the expansion length of the first airbag increases in the direction of the driver, while the diameter or collision zone of the first airbag is naturally reduced. The second airbag can be filled with different gas quantities by a controllable gas source, preferably one that can be activated in stages. The shape of the two airbags and the deformation of the first airbag can therefore be set.
Elastic shaping elements, such as restraining straps, in the first airbag permit the first airbag to be deformed and returned to its original shape when the outer, second airbag deflates and the gas pressure in the first airbag also drops.
The first airbag preferably has a slight deflation or a longer inflated period, which is why it can be deployed early and offer sustained protection. The second airbag, which is preferably only deployed if a second acceleration threshold is exceeded, offers the greatest possible protection, but deflates faster,,and therefore only briefly impedes the driver""s visibility when deployed.
A passenger-protection apparatus of this type and a device for detecting the size and/or position of the passenger can be combined into a deployment method in which the first airbag is deployed particularly early when a first, very low, acceleration threshold is exceeded, regardless of the size and/or position of the passenger, and the second airbag is deployed, as a function of the size and/or position of the passenger, when a second, higher acceleration threshold is exceeded. The first airbag protects the passenger without endangering him in xe2x80x9cout-of-positionxe2x80x9d situations, and without impeding visibility. The detection device has sufficient time for deciding whether and to what extent the second airbag will be deployed.